The construction of semiconductor nanocrystal (SNC)-based composites is of fundamental importance for various applications, including telecommunication, lasers, photovoltaics, and spintronics. The major challenges are the intentional insertion of dopants into SNCs for expanding their intrinsic functionalities and the scalable incorporation of activated SNCs into host free of hydroxyl and organic species for stabilizing and integrating their performances. An in situ approach is presented to couple the SNC doping and loading processes through self-limiting nanocrystallization of glassy phase, enabling one-step construction of fully transparent Ga2O3 SNC–glass nanocomposites. It is shown that the intentional introduction of various cation/anion impurities (e.g., F−, In3+, and Ni2+) or their combinations into Ga2O3 SNCs can be realized by taking advantage of the viscous glass matrix to enhance the desorption barrier of impurity on the SNC surface and strengthen its tendency to incorporate into the SNC lattice. The composite can be rationally activated to show wavelength-tunable and broadband luminescence covering the spectral ranges of near ultraviolet, visible, and near-infrared wavebands. The approach is predicted to be general to other SNC materials for functional modulations and will be promising for scalable fabrication of novel SNC-based composites.